Thermostatic circuit closer



sept. 11, 1934. G. H. BRADS( 119172,975

THERMOSTATIC CIRCUIT CLO'SER Filed Nov. 12 195o ammi Geoyelfm, l

Patented Sept. 11, 1934 UNITED STATES PATENT.' OFFICE Improved Fire more, Md.

Detector Corporation, Balti- Applicaton November 12, 1930, Serial'No. 495,255

6 Claims. (Cl. 20a-138) 'I'his invention relates to certain new and useful improvements in thermostatic circuit closers, and

particularly circuit 'closets of that type in which the circuit closing action/is effected by the bowing movement of a bimetallic contact strip having a contact portion movable into engagement with a pointed contact member. The invention may, for example, be embodied in such a type of thermostatic circuit closer as that disclosed in 10 my prior application iiled February 18, 1929, Serial No. 340,892. In the use of such thermostatic circuit closers in a fire alarm system, it is the general practice to fix thecircuit closing device on the ceiling or a support adjacent to the ceiling, so that the thermostatic strip will be iniluenced by the rising -heated air whena fire breaks out in the guarded room or apartment in which the thermostat is arranged. The contact member and circuit closlng strip are commonly made of certain metals which are subject to surface oxidation or corrosion interferingI with a good electrical contact, and to prevent such oxidation the contact member and strip may be provided with a coating of 26 a non-oxidizable metal. It is difficult, however, to prevent corrosion in cases where the circuit closer is exposed to the action of sulphric or nitricl or other acid vapors or chlorine or other.

gases in the atmosphere, and it is also impossible 30 to construct the circuit closer so that it will be absolutely proof aganstthe coating of the contact surfaces by mist-like deposits of paints or other wall coatings dissipated into the atmosphere in paint spraying actions.

For these reasons, the Underwriters Laboratories standards require that the stationary contact member and contact portion of the contact s trip be so guarded or constructed as to protect the same from oxidation, corrosion or deposits of electric-insulating substances thereon, and/or that the contact elements have such an action as to ensure a good physical contact for a positive circuit closing operation when the thermostatic strip moves into engagement with the contact member.

'Ihe object of my invention is to provide a thermostatic circuit closer with a contact member and a thermostatic contact strip provided with contact surfaces which are proof against the action of oxidizing or corrosion inducingsubstances.

A further object of my invention is to provide a thermostatic circuit closer in which the circuit closing contact member and contact portion of'the thermostatic strip are so constructed and arranged as to secure a wiping action of the strip with the contact 'member when the strip moves into engagement therewith, so that, even in the event of the deposit of a coating of insulating material upon the contact surfaces, such coating will be scraped off and a good electrical contact obtained.

'Ihe invention consists of the features of construction, combination and arrangement of parts, hereinafter fully described and claimed, reference being had to the accompanying drawing, in -y whichz Fig. 1 is a horizontal transverse section through a circuit closer of the type described embodying my invention.

Fig. 2 is a vertical longitudinal section through 70 the same, looking toward the slotted side of the casing body tovwhich the circuit closing device is applied.

Fig. 3 is a vertical transverse section on the line 3-3 of Fig. 1, showing the outer end of the 75 contact screw as it appears before it is cut off.

Fig. 4 is a view similar to Fig. 3 showing the outer end of the contact screw cut off.

Fig. 5 is a view showing the normal relative positions of the contact member or screw and contact end of the thermostatic strip when the circuit is normally open.

Fig. 6 is a view similar to Fig. 5 showing the contact screw or member and contact strip in circuit closing contact.

Referring now more particularly to the drawing, 1 designates a ventilated casing comprising a. longitudinally channeled body, formed of sheet metal, and having a back wall 2 and side walls 3, said casing body being normally open at its ends and front side. As shown, the walls 3 are provided with flanges 4 bent inwardly toward each other at the front side of the casing body for the purpose of reducing the width of the front opening and retaining in position a perforated cover plate or iront wall member 5. The cover plate is also made of sheet metal, and comprises a body portion which is preferably transversely arched and closes the opening between the flanges 4, said cover plate being overhung at its lateral edges by said flanges so as to be retained from outward displacement. The cover plate is provided with angularly bent portions 6 terminating in right angularly bent perforated attaching projections or ears '1, whereby the circuit closer 105 may be fastened at the point of use to the ceiling of a room or other suitable support. The parts 6 of the cover plate are so arranged as to'close the ends of the channeled casin`g,\and said plate and One of the side walls 3 of the casing body are re- 11g Cil spectively provided with ventilation openings 8 and 8a to allow the heated air, when a conagration occurs, to pass into the casing so as to be connedtherein to cause the thermostatic strip to bow for a circuit closing action.

The side 3 of the casing body opposite that in which the perforations 8a are formed is provided with a pair of spaced longitudinal slots 9 separated by an intermediate intact portion or bridge piece 10. On this side of the casing is mounted an insulated carrier strip or support 11 for the current carrying parts of the device. This carrier or support comprises an oblong rectangular block or strip of suitable electric insulating material. On the outer face of this strip 11 are mounted terminal plates 12 and 13 of phosphor bronze or other suitable material, and on the inner face of the strip is arranged a supporting block 14 arranged opposite the terminal plate 13. The terminal plate 12 is' secured in position by screws l5 and 16, while the terminal plate 13 and the block 14 are secured in yposition by screws 17 and 18. The screws 16 and 17, the former of which passes through the strip 11 and the plate 12, and the latter of which passes through the plate 13, block 14 and strip 11, are provided with binding washers 19 and binding nuts 21.

The screw 15 has a conical or pointed inner end 21 projecting beyond the strip 11 and through one of the slots 9 into the casing, said conical end of the screw providing a preliminarily adjustable but normally iixed circuit closing contact. Arranged within the casing for coaction therewith is a bimetallic strip 22 composed of two metals of different coeciencies of expansion and contraction. These metal strip members are coextensive in length and welded together and are jointly secured at one end by the screws 17 and 18. 'Ihis strip may be provided with a coating of a suitable material to protect the same from oxidation and corrosion, such, for example, as a coating of chromium. The screw 15 is provided with ne or micrometer screw threads, the threaded portion of said screw engaging threaded openings in the strip 11 and plate 12. Initially the outer end of the screw projects, as shown in Figs. 1 and 3, a suitable distance beyond the outer face of the plate 12 and is provided with a nick or other means 23 whereby a screwdriver or other suitable tool may be engaged therewith to secureV 'it in position. The screw body is preferably made of soft metal so that after having once been set or adjusted its outer end or projecting portion may be cut off ush with the outer face of the plate 12, so as to prevent accidental displacement of said contact screw from its said position or meddlesome persons turning it and changing its position.

The pointed end 21 of the screw 15 lies in the path of movement of the free end of the strip 22, when the latter is bowed or deiiected in one direction by the action of heat at a certain predetermined temperature, so that when the strip is thus bowed the free end of the strip will be brought into engagement with the pointed end of the screw for a circut closing action.

The carrier or support 11 is adapted to be detachably secured in position by fastening screws 24 securing it at its ends to the casing wall beyond the slots 9 and an intermediate screw 25 securing it to the bridge piece 10. It will be observed that all the current carrying connections are mounted upon the common insulated support or carrier strip 11, which is detachably secured to the slotted wall 3, and which provides for the mounting of all the current carrying connections upon, or the dismounting of said current carrying connections from, the casing ina simple and convenient manner, and so that when the parts are assembled all of the current carrying parts will be insulated from the casing. In the device as organized for use the contact pin 15v lies within one of the slots 9, free from connection with the casing, while the block 14 projects through the other slot 9. In applying the unitary current carrying structure to the casing body, said current carrying structure is brought into position on the exterior of the slotted side 3 so that the free end of the strip 22 will be in alinement with the slot 9 to be occupied by the block 14, whereupon such end of the strip 22 is inserted into the casing body through said slot and the current carrying unit then moved longitudinally in the direction toward the other slot 9 until the block 14 comes opposite the slot 9 through which the strip 22 has been introduced, after which the current carrying unit is simply moved inward to bring the parts thereof into working position and secured in place by means of the screws 24 and 25. When it is desired to remove the current carrying unit, all that is necessary is to unfasten the screws 24 and 25 and to shift the unit llongitudinally in the reverse direction to that in which it was introduced and then to withdraw it laterally, as will be readily understood. When the device is disposed in use, as upon the ceiling of a room, to which it is attached by the ears or fastening member "I, the body of the casing will be spaced from the` ceiling to allow heated air to circulate completely around the device and to dispose the binding posts at a safe distance from the ceiling, and so as to allow them to be more conveniently reached when required, while 'the perforate front wall or cover plate will face downwardly so that the heated air from below may ow freely through the perforations 8 and 8a into the casing and be confined for a period, thus, in case of a conagratin, providing for the morecertain exposure of the thermostatic circuit closer 22 to the rising heated currents of air.

In. accordance with my present invention, the pointed contact portion 21 of the contact screw or member 15 is made of an alloy of gold and silver which will not oxidize or corrode under the action of corrosion inducing acids or gases of the character described. Also the strip 22 has its free end bent to form a contact surface 26 carrying a Contact button or member 27 tted and secured in an opening therein, which contact member or button may be made, like the point of the screw, of an alloy of gold and silver for the purpose described. The end 26 of the strip 22 is bent at an oblique angle thereto and at such an angle that in the movement of the strip toward the contact point 21 from the open position shown in Fig. 5 to the closed p'osition shovm in Fig. 6, the contact member 26 and its contact button 27 will be bowed, as shown in Fig. 6, and move in such an arc toward the contact point 21 that the distance between the fixed end of the strip and the contact 27 will be shortened so that a wiping action of part 21 on contact 27 will occur. Preferably this wiping action is increased by making the range of circuit closing motion of the end 26 of the strip 22 of a distance greater than the distance normally between such en d of the strip in its open position and the contact 21, so that the bowing of the strip will continue for a certain time after contact is made, with the result that the face of the button 27 will be drawn across the extremity of point 21 to obtain a strong rubbing or wiping contact. This rubbing or wiping contact will be of such character that, even in the event that there should be a film or coating of an insulating material on the face of the button 27, said lm or coating will be `scratched oi, so that there will be an absolute metal to metal contact between the parts 21 and 27 to ensure a certain and positive conducting engagement of the contacts and closing of the electric circuit. y

From the foregoing description, taken in connection with the drawing, the construction and mode of Operation of my improved circuitclosing device will be readily understood and it will be seen that the invention provides a means for securing a positive engagement between the circuit closing contacts even under conditions where the contacts are coated with a lm of dust, paint or other wall coating material, or are effected on the surface by oxidation or corrosion, so that all requirements in this connection will be effectually met for the provision of a circuit closing device which will be absolutely positive in action under the conditions mentioned.

Having thus fully described my invention, I claim:-

l. In a thermostatic circuit controller, a support, a circuit contact element, and a resilient bimetallic circuit opening and closing strip adapted to bow at a predetermined temperature and mounted on said support so as to have a free end portion arranged for circuit make and break coaction with said contact element, said free end portion of the strip being provided with a contact terminal-projecting laterally at an angle to the body of the strip in the direction reverse to the bowing direction of the strip, said contact terminal of the strip being normally spaced from said circuit contact element and so related thereto that in the bowing action the strip will be shortened and in the shortening action its said contact terminal will be drawn with a wiping engagementacross the contact element for a circuit closing action therewith.

2. In a thermostatic circuit closer, a support, a

circuit contact element having a contact end tapering to a point, and a resilient bimetallic circuit closing strip adapted to bow at a predetermined temperature and mounted on said support so as to have a free end portion provided with a contact terminal projecting laterally at an angle to the body of the strip in the direction reverse to the bowing direction of the strip, said contact terminal of the strip being normally spaced from saidcircuit contact element and so related thereto that in the bowing action the strip will be shortened and in the shortening action its said contact terminal will be drawn across the pointed end of the contact element for a circuit closing action therewith.

3. In a thermostatic circuit closer, a support, a circuit contact element adjustably mounted on the support and having a contact end tapering to a point, and a resilient bimetallic circuit closing strip adapted to bow at a predetermined temperature and mounted on said support so as to have a free end portion provided with a contact terminal projecting laterally at an angle to the body of the strip in the direction reverse to the bowing direction of the strip, said contact terminal of the strip being normally spaced from said circuit contact element and so related thereto that in the bowing action the strip will be shortened and in the shortening action its said contact terminal will be drawn across the pointed end of the contact element for a circuit closing action therewith, the adjustable mounting of the contact element adapting said contact element to be variably spaced with relation to the contact terminal to vary the time period of the circuit closing action.

4. In a thermostatic circuit closer, a support, a circuit contact element having a pointed tip of a non-oxidizable metal, and a resilient bimetallic circuit closing strip adapted to bow at a predetermined temperature and mounted on said support so as to have a free end portion provided with a contact terminal projecting laterally at an angle to the body of the strip in the direction reverse to the bowing direction of the strip, said contact terminal of the strip carrying a non-oxidizable contact piece and being normally spaced from said circuit contact and so related thereto that in the bowing action the strip will be shortened and in the shortening action the contact piece of its said contact terminal will be drawn across the tip of the contact element for a circuit closing action therewith.

5. In a thermostatic circuit closer, a support, a circuit contact having a pointed end, and a resilient bimetallic circuit closing strip adapted to bow at a predetermined temperature and fixed at one end to said support and having a free end contact portion projecting laterally at an angle to the body of the strip in the direction reverse to the bowing direction of the strip, said contact portion of the strip being normally spaced from said circuit contact and so related thereto that in the bowing action the strip will be shortened and in the shortening action its said contact portion will be drawn across the pointed end of the contact for a circuit closing action therewith.

6. In a thermostatic circuit closer, a support, a non-oxidizable circuit contact element having a contact end tapering to a point, and a resilient circuit controlling strip formed of metals having different coeicients of expansion adapting it to bow at a predetermined temperature, said strip being mounted on said support so as to have a free end portion forming a contact terminal for coaction with the pointed contact end of the circuit contactelement, said terminal comprising integral portions of the metal components of the strip bent laterally at an angle to the body of the strip and provided with a contact piece `of nonoxidizable material, said contact terminal being so related to the contact element that in the bowing action the strip will be shortened and the contact' terminal moved to draw its contact piece with a wiping action across the pointed end of the contact element.

GEORGE H. BRADY. 

